Induction furnace



June 1, 1943. J, R, WYATT 2,320,692

INDUCTION FURNAGE INVENTOR 9mm R nl?" BY w v ATTORNEY June 1, 1943. v 1R, WYATT 2,320,692

INDUCTION FURNACE 2 Sheets-Sheet 2 Filed Sept. 19, 1941 INVENTORATTORNEY i PatentedJune 1, 1943 UNITED STATES PATENT GFFICE INDUCTIONFURNACE James R. Wyatt, Llanerch, Pa., assignor to Ajax Electric FurnaceCorporation, Philadelphia, Pa., a corporation of PennsylvaniaApplication September 19, 1941, Serial No. 411,461

7 Claims.

This invention deals with electric furnaces of the submerged resistortype and has for its purpose the improvement in circulation of moltenmetal in the melting channels of such furnaces.

A purpose of the invention is to provide a furnace of the classdescribed having plural primary coils and plural melting channels orsecondary loops so arranged on a common iron core assembly that therepulsion force due to end ellect on the melting channels by theirrespective primary coils and the attraction forces due to interaction ofadjacent melting channels on each other can be superimposed to create anenhanced and controllable pressure differential on molten metal in therespective melting channels for circulating same.

A further purpose is to provide a furnace of the classdescribed having astrong unidirectional circulation in the melting channels.

A further purpose is to provide a furnace of the class describedin whichthe degree of stirring may be controlled as a function of the way inwhich the lining is formed or by variation in the electrical connectionsto the primary coils or by variation of the location of the primarycoils with respect to the melting channels.-

Further purposes will appear in or be evident from the speciilcation andthe claims.

Figs. .1, 2 and 5 are diagrammatic representations oi' the principalelements involved in a furnace of the type described, and are used inconjunction with the description to illustrate the effect 'on thecirculation forces of the relative location of secondary loops withrespect to the primary coils.

Figs. 3'and 4 are cross section elevation and plan views of a furnacebuiltin accordance with the present invention.

Fig. 6 is a wiring diagram showing secondary loops in diagrammatic formand is used in conand primary inducing winding. In operation, when theprimary winding is excited current is induced into metal in the meltingchannel which heats same and which because of the electrical repulsionand pinch effect forces ejects the metal from the melting channel intothe hearth proper and around colder metal in that portion of thefurnace.

As hot metal is expelled from the melting channel a circulation is setup and colder metal is supplied to the channel.

The circulation of metal from and to the melting channel is a functionof many variables and will fail.

junction with the description to show how clr' culation control may beobtained electrically by varying end eiect reactions between primary andsecondary loops.

The type of furnace to which the present invention is applied is wellknown to the industry and has been amply described in previous patent villes. Applicants patents U. S. .1,201,671 and Re. 16,967 are referredto. The present invention is an improvement over the typesheretoforevdescribed.

The submerged resistor furnace .comprises a hearth for holdingv moltenmetal, a depending melting channel or secondary loop opening into ,saidhearth and adapted to surround an iron core The most successful designwhich has heretofore been developed is one in which a two Waycirculation takes place. IThe legs of the melting channel meet at apoint low in the furnace and the design is such that a strongcirculation takes place upward on the outside portion of each leg anddownward on the inside portion. Circulation in the two legs is vigorousand extends almost to the low point.

It has been the goal of designers of furnaces of the submergedresistortype to design a furnace wherein the metal in the meltingchannel can be made to flow in a unidirectional manner. U. S.

Patent Re. 16,967, above referred to, probably describes the bestattempt made thus far to achieve this', but although a unidirectionalcirculatlon has been achieved it has not yet been made suiilcientlyvigorous for practical fast melting operations.

In the present specification applicant describes an improvement over theolder methods whereby he is enabled to obtain a much better control overthe two way stirring andv whereby, if desired, he can obtain a veryvigorous unidirectional circulation; an improvement which he believeswill contribute materially toward the development of larger and fastermelting furnaces. As the coil spacing and forces for unidirectionalstirring are more complex than for the ordinary-two way stirring most ofthe destirring effect.

Adiscussion of the forces involved which ap' plicant utilizes to.produce a strong unidirectional circulation or flow in the melting loopof a submerged resistor furnace follows:

Referring to Fig. 1, a primary coil I, having an n insulating sleeve andend pieces 2, surrounds an iron core member 3. Leads 4 connect the pri-`mary coil to a source of alternating current power, not shown. Asecondary loop 5 is adapted to surround the primary coil and core andrepresents what would be the melting channel in an actual furnace. Intests made by applicant this loop comprised a single turn of heavycopper tubing adapted with water cooling means so that the mechanicalforces involved could be studied without overheating of the parts. Whenthe secondary loop is placed in the position shown about the middle ofthe primary coil no mechanical forces are evident. There is of course amechanical force in a direction radially out from the axis of theprimary coil but this is equal in all directions. As the secondaryloopis moved toward the end portion of the coil as at 5 there is a verystrong mechanical force tending to push it entirely off of the end andout of the electromagnetic field of the coil. This force is exertedateither end of the primary coil even though the secondary loop is stilllinked electromagnetically by the iron core.

If the secondary loop 5 is moved so that one part 'of it is near the endof the primary coil and another part is near the center of the coil themechanical force set up'in it will tend to be great in the direction ofthe axis of the coil where it is near the endof the coil and will be lowWhere it is near the center of the coil.

If two secondary loops are put close together around a single primarycoil a mechanical force is exerted which tends to pull them together.This is due to the proximity effect or reaction of the secondaryelectromagnetic fields around conductors carrying current in the samedirection.

In Fig. 2 two secondary loops 5 are adapted to be placed around twoelectrically identical primary coils I, having respective end parts 2and a common iron core 3.` When the loops are placed near the centers oftheir respective primary coils no mechanical force due to end effect isnoticeable. There is some end effect on each loop due to the adjacentprimary coil but this force is very little beyond the end of the coiland can be disregarded. Similarly, when the secondary loops are near themid points of their respective coils the effect of one loop on the otheris negligible because of the distance between them. This force also canbe disregarded.

In the instance described with reference to Fig. 2, it should :be notedthat even though the respective primary coils are electrically identicaland even though they are placed very close toether the leakage fieldsabout each are so great that the combined effect as regards mechanicalforces set up in the secondary loops is about the same as for two widelyseparated single coil assemblies. It is the utilization of thischaracteristic which forms the basis of applicants' present' invention,as by combining the end effect repulsion and the proximity effectattraction of the two secondary loops he has been able to obtain aconsiderably greater mechanical force and a better method of controllingthat force than has heretofore been described, whether the desiredstirring is unidirectional or two way.

In Fig. 2, when the secondary loops 5 are in the positions shown by thesolid lines, each absorbs power from its primary coil much as in thestandard single coil furnace. The only forces exerted are in a radialdirection from the axis of the core. The reactions on the secondaryloops from the adjacent primary coils and the reactions between thesecondary loops themselves are practically negligible. The total resultsare quite similar to what would be expected if the two coils were madeinto one continuous coil threading the two secondary loops.

If the two secondary loops are brought together near the point where thetwo primary coils meet and as they approach each other over the ends oftheir respective coils, end effect on each secondary loop, by itsprimary coil, begins to become evident and the loops are vigorouslypushed toward each other. As they approach each other the proximityeiiect due to the reaction of each loop on the other becomes effectiveand the loops are also pulled together by this force. By thisconstruction the repulsion and attraction forces are superimposed and avery strong -total force is exerted tending to hold the secondariestogether. Both forces are of a major nature and even with the simpleapparatus used in test the force exerted was so strong'that one couldnot move the loops apart or hold them apart without mechanical aids.

Where two such secondary loops are energized by a single primary coil,no end effect forces are evident and the attraction of each loop by theother, while as great as-in the two coil instance, is not nearly sogreat as the combined forces obtainable, and cannot be controlled as canthe two coil effect.

If the two loops of Fig. 2 are placed in the positions shown v'by thedotted lines the end and proximity effects are great where they areclose near the ends of their respective primary coils but are low ornegligible where they are spaced near the centers of their respectiveprimary coils.

The mechanical forces which have been described with reference to Figs.l and 2 can be measured but Itheir effect on the circulation of metal inthe melting channels of a submerged resistor furnace does not becomeevident until the loops are opened and arranged as in an actual furnace.

In Figs. 3 and 4 a melting furnace is shown in which the mechanicalforces heretofore described are incorporated. In these Mures applicanthas provided a hearth having refractory walls 6, secondary loops ormelting channels 1, in the lower part of the furnace and primary coils 8surrounding an iron core assembly 8. As in the dotted lines in Fig. 2the melting channels or secondary loops 1 are placed close together andnear the ends of their respective primary coils at one side-of thefurnace and for apart or near the mid portions of the same coils at theother side of the furnace. They are here shown as rectanA gular tubeshaving a smaller cross sectional area where they are closer togetherthan elsewhere, although this is not a primary consideration. Anotherfeature of the construction as shown, which is desirable but notrequired, is that the melting channels or secondary loops are spacedfurther from their respective primary coils at the point where they areclose together and join the furnace hearth.

The usual appurtenances which aie customary for a furnace of this typesuch as power supply, switches, casings, support members, trunnions fortilting the furnace, etc., have been omitted With the construction shownin Figs. 3 and the primary coils when energized will induce currentwhich will flow through the metal in the secondary loops and the hearth.Because of the shapes of the loops this current will be crowded in therestricted portions, and be less dense elsewhere in the loops andhearth. The electromagnetic fields set up about the primary coils andsecondary loops will be greatest and the reactions will be greatestwhere these restricted portions are close together.

A maximum pressure will be produced at the point where the loops areplaced close to each other which is due to the superimposing of thefollowing forcesthe end effect of each primary coil on its secondaryloop tending to push the metal in the two loops toward each other; theproximity or attraction force due to th'e reaction of each secondaryloop on the other tending to pull the metal in each loop toward theother and adding directly to the aforementioned end effect;

, the repulsion effect due to reaction between each secondary loop andits primary coil, tending to force the metal radially away from thetransformer axis; the pinch effect force due to the current induced intoeach secondary loop by the primary coils and tending to force the metalin both directions along the loop from the point of greatest currentconcentration, and the 'funnel effect due to unequal distribution ofcurrent in a cone shaped inductor tending to cause the metal in the loopto iow along the center of the loop section fromI the restricted pointtoward the less restricted points. Other forces such as motor effect dueto reaction on the secondary loops by the primary coils and vby otherparts of the secondary loop itself may be utilized. That these forcesare of a definite and useful nature is due primarily to thesuperposition on the other forces of the forces due to end effect, whichheretofore have not been considered `in Ithe construction of submergedresistor melting furnaces.

In the furnace described the forces combine to move the liquid metalfrom the hearth through the melting or secondary loops and back into thehearth. The direction of circulation is counterclockwise from thesection of greater to sections of lesser pressure. In the instancecited, there will be some tendency for and possibly some eddy flow ofmolten metal in a clockwise direction, or uplward from the point in thechannel or loop marked X, due to the pinch effect force, butsubstantially all of the other forces, including an equal component ofthe pinch effect force, will tend to make the metal flow in thecounterclockwise direction.

Since the forces utilized in applicants present invention usually becomegreater as the melting channel or loop sections are placed closertogether applicant believes that in some instances they can be actuallyjoined without detriment, and that even greater current concentrationsand circulation may be effected by so joining them.

InvFig. 5 applicant has shown four secondary loops or melting channelsand four primary coils so arranged that each of the four loops isaffected by end effect forces at one point in itspath and so that thefour secondary loop sections so affected are spaced close to each otherwhereby each tends to exert an influence on the other three. In thisfigure the individual loops could be joined to form a single loopsection as at the dotted circle C.

While the -feature of unidirectional circulation .has been describedvery fully in this specification lation. Some such arrangements are forcoils of unequal mechanical or electrical design; for single orpolyphase or other multi-coil constructions; for separate magnetic coreassemblies; for variations in secondary loop shape or section, and thelike. These are deemed but variations of applicants invention and it isnot believed a full list ofsuch possibilities is here necessary.

The characteristics of a furnace of this type depend largely on thelocation and shape of the melting loops with respect to the primaryinducing coils and can be widely controlled for different types of metalmelting or for different melting speeds by varying the secondary loop ormelting channel arrangements while the linings are being installed. Thusfor fast or for high temperature melts the circulation must be higherthan for slow or low temperature melts. Then too there is some advantagefrom the efficiency standpoint in not having more circulation than isrequired for a given melt.

Some'control may be built into the furnace proper to allow for makingelectrical or mechanical changes during the operation of the furnace.The most common is by control of voltage on the primary coil and isaccomplished by external voltage control or taps on the primary coils.In some instances the relative location of coils and melting loops maybe changed mechanically by shifting the location of the primary coilswith respect to the'secondary loops as illustrated in Fig. 1. In otherinstances the relative locations of primary coils and secondary loopsmay be lshifted electrically as by some such circuit as shown in Fig. 6.

In Fig. 6 are shown two primary coils I and two secondary loops 5,surrounding an iron core piece 3. The secondary loops are arranged to besufficiently close in one section of their path to react with eachother, but are spaced sufficiently inside the ends of their respectivecoils so that when these parts of the primary coils are energized no endeffect results. The primary coils are so arranged 4that lengths A canbeenergized in which case the end effect force is not great, or so thatlengths B can be energized bringing the end effect force into play.'I'he parts of the coil to be used can be controlled by the switch l0effecting a circulation control without materially affecting the powerinput to the melt.

Applicant believes that in designing a furnace to utilize end effect inconjunction with the other forces available for causing circulation in asubmerged resistor furnace he has greatly advanced the possibilities forextending the use of such furnaces into fields ofv larger and fastermelting. He believes that his invention herein described is new andpatentable and requests that U. S. Letters Patent be granted to him forall that is claimed. as follows:

1. An electric furnace of the submerged resistor type comprisingrefractory walls, a hearth. a plurality ofrmelting channels opening inand depending from said hearth, a separate but electrically generallysimilar primary coil associated with each melting channel, each saidmelting channel having a portion positioned substantially at and otherportions spaced from an end of its respectiveprimary coil, said portionsnear the coil ends being positioned close to each other.

2. An electric furnace of the submerged resistor typecomprisingrefractory walls, a hearth, a plurality of melting channels opening intoand depending from said hearth, a primary coil associated with eachmelting channel, a common iron core threading the primary coils andmelting channels, each of said melting channels having a portionA ofVrestricted section as compared with other'sections said portions beingpositioned close to each other and each said portion being ,positionedcloser to an end of its respective primary coil than other portions ofthe same melting channel.

3. An electric furnace of the submerged resistor type comprisingrefractory walls, a hearth, a pair of melting channels opening into anddepending from said hearth, a pair of substantially identical primarycoils placed adjacent to each other around a common iron core, eachassociated with one of said melting channels, each of said meltingchannels having a portion of restricted section as compared with othersections, said portions only being positioned close to each other andclose to the adjoining ends of their respective primary coils. l 4. Inan electric furnace of the submerged resistor type comprising refractorywalls, a hearth, a pair of melting channels opening into and dependingfrom said hearth, a pair of Isubstantially .identical primary coilsplaced around opposite legs of a common iron core each associated withone of said melting channels, each of said melting channels having aportion of restricted section as compared with other sections, saidportions only beingvpositioned close to each other and close to an endof their respective primary coils.

5. An velectric furnace of the submerged resistor type comprisingrefractory walls, a hearth, a pair of melting channels opening into anddepending from said hearth, said channels being closely spaced at oneside of the furnace and widely spaced at the other side of the furnace,a

pair of substantially abutting primary coils surrounding a common ironcore and threading said channels, the lengths of said coils being suchthat they extend Well beyond the secondary channels on their extremeends and beyond said channels on their abutting ends and electricalswitching means for optionally energizing the coils except for portionsat the abutting ends or except for portions at the extreme ends.

6. An electric furnace of the submerged resistor type comprisingrefractory Walls, a hearth, a pair of melting channels opening into anddepending from said hearth, a pair of primary coils, similarly connectedto a single phase source of alternating current, placed end to end andclose to each other around a common iron core, each associated with oneof said melting channels, said melting channels being positioned atleast in part close to each other and close to the adjoining ends oftheir respective primary assemblies.

'7. An electric furnace of the submerged resistor type comprisingrefractory Wal1s,a hearth, a pair of melting channels opening into andde- 'pending from said hearth, a pair of primary coils, similarly,connected to a single phase source of alternating current, placed end toend and close to each other around a common iron core, each associatedwith one of said melting channels, said melting channels beingpositioned close to each other and close to the adjoining ends of theirrespective primary assemblies.

JAMES R. WYATT.

